1. Field of the Invention
This invention relates generally to poly(arylene sulfide) composites, and more particularly, to poly(arylene sulfide)/carbon fiber composites having improved adhesion between the resin matrix and the carbon fibers in the composite.
2. Description of the Prior Art
It has long been appreciated that good adhesion between the resin matrix and the reinforcing fibers utilized in composite material is necessary. The usual means employed for enhancing adhesion between the fibers and the resin matrix has been to use a sizing composition to coat the fibers before consolidation with the resin matrix.
Sizing compositions operate in generally one of two ways to aid adhesion. The sizing composition may be chemically active and react to form a chemical bond between the fibers and the matrix, or it may form a more compatible surface on the fibers such that the matrix will more readily spread out on and adhere to the fibers. Where the reinforcing fibers have been glass fibers, compositions containing silanes have been successfully employed as sizings to link the glass fibers and the resin matrix.
The use of carbon fibers in composites has involved different approaches. In the preparation of the better known and older thermoset resin matrix/carbon fiber composites, a number of proprietary sizing compositions have been employed with varying degrees of success. In recent years there has been a growing interest in composites employing thermoplastic resin matrices and carbon fibers. Much of this interest is due to the generally greater processability and shelf life of thermoplastics as compared to thermoset resins as well as to the greater chemical resistance and moisture resistance of thermoplastics such as the poly(arylene sulfides).
Well known poly(arylene sulfides) are poly(phenylene sulfide) and poly(phenylene sulfide/sulfone) which are commercially available under the trademark RYTON.RTM. from the Phillips Petroleum Company, Bartlesville, Okla. Such resins are particularly suitable for use in composites because of their excellent rigidity and heat and electrical resistance as compared to other thermoplastic resins.
Thermoplastic resins, however, pose a number of problems in terms of obtaining composites with good adhesion to reinforcing carbon fibers. The same chemical resistance and relatively low chemical activity which make thermoplastics such as poly(phenylene sulfide) and poly(phenylene sulfide/sulfone) attractive for use in composites, also inhibit effective adhesion to carbon fibers through chemical bonding. Most thermoplastic resins are of a more viscous nature than thermoset resins, and therefore do not physically spread onto carbon fibers as well as thermoset resins. Also, most of the sizing compositions that have been traditionally employed in the thermoset resin composites degrade at the temperatures required to process thermoplastic resins such as the poly(arylene sulfides). Thus, there is a need for a method of producing thermoplastic resin/carbon fiber composites having improved adhesion between the thermoplastic matrices and the carbon fibers as well as for the composites so produced, particularly carbon fiber composites formed of poly(arylene sulfide) and poly(arylene sulfide/sulfone) resins.